The colour blue is typically associated with a range of emotions and states of being including: calmness, purity, truth, wisdom, depression and peace. Different people perceive colours in different ways, so you may have other associations, which are equally valid.
In Buddhism blue is linked to wisdom, and in Hebrew traditions it's associated with mercy. Both Christ, and the Virgin Mary, have both been depicted wearing shades of blue, representing their detachment from worldly goods, materialism and possessions. Blue is the colour of the sky and as such is associated with a sense of peace, freedom and calmness.
The ancient Egyptians regarded blue as being the colour of truth, and the images painted on the walls of their tombs were on a sky-blue background. It's also a colour that's been linked to scores of gods, particularly sky gods, such as the Egyptian Amun, the Greek Zeus, Roman Jupiter, the Hindu Indra, Vishnu and his incarnation, Krishna (who was said to have blue skin).
When people are feeling low in spirits or depressed they're often said to be, "feeling blue." It's thought this phrase may stem from the twilight blues songs sung by African slaves whilst being held captive in North America.
In the case of the chakras, blue represents the throat chakra.
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